Re: MERGE SQL Statement for PG11

On Sat, Oct 28, 2017 at 12:49 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> Nothing I am proposing blocks later work.

Actually, many things will block future work if you go down that road.
You didn't respond to the specific points I raised, but that doesn't
mean that they're not real.

> Everything you say makes it clear that a fully generalized solution is
> going to be many years in the making, assuming we agree.

I think that it's formally impossible as long as you preserve the ON
CONFLICT guarantees, unless you somehow define the problems out of
existence. Those are guarantees which no other MERGE implementation
has ever made, and which the SQL standard says nothing about. And for
good reasons.

> "The extent to which an SQL-implementation may disallow independent
> changes that are not significant is implementation-defined”.
>
> So we get to choose. I recommend that we choose something practical.
> We're approaching the 10 year anniversary of my first serious attempt
> to do MERGE. I say that its time to move forwards with useful
> solutions, rather than wait another 10 years for the perfect one, even
> assuming it exists.

As far as I'm concerned, you're the one arguing for an unobtainable
solution over a good one, not me. I *don't* think you should solve the
problems that I raise -- you should instead implement MERGE without
any of the ON CONFLICT guarantees, just like everyone else has.
Building MERGE on top of the ON CONFLICT guarantees, and ultimately
arriving at something that is comparable to other implementations over
many releases might be okay if anyone had the slightest idea of what
that would look like. You haven't even _described the semantics_,
which you could do by addressing the specific points that I raised.

--
Peter Geoghegan